Aqueous phototransformation of diazepam and related human metabolites under simulated sunlight.

Phototransformation of the widely used benzodiazepine pharmaceuticals diazepam and human metabolites nordiazepam, temazepam and oxazepam under simulated sunlight in water was investigated. Photolysis experiments were conducted in the presence and absence of humic acids. Half-lives for each of the benzodiazepine pharmaceuticals were <200 h (under all conditions) suggesting that phototransformation is an important process for such chemicals in the photic zone of receiving waters. Due to the observed phototransformation of the benzodiazepines, significant emphasis was placed on identification of the photoproducts. A total of fourteen photoproducts, including benzophenones, acridinones and quinazolinones or quinazolines was identified and measured by liquid chromatography-multistage mass spectrometry (LC-MS(n)). Phototransformation studies were also undertaken on authentic samples of two of the identified photoproducts, 5-chloro-methylaminobenzophenone and 2-amino-5-chlorobenzophenone, in order to establish the phototransformation pathways. Interestingly, these two photoproducts showed relatively higher persistence than some of the benzodiazepines, suggesting that the fate and effects of photoproducts should also be incorporated into future risk assessments and environmental models of the fate of benzodiazepines.